PURPOSE: To quicken the start of normal operation of the title circuit by using a charging means so as to charge the 1st and 2nd capacitors quickly by means of the charging means after application of power, utilizing the property of a diode after a prescribed time and separating electrically the 1st capacitor and the 2nd capacitor.

CONSTITUTION: When a voltage is applied to a power line 10 after application of power, the charge is stored and a voltage depending on the voltage division ratio of each capacitor is generated momentarily at each terminal of the coupling capacitor 3. The capacitance of each capacitor is selected so that the said voltage is equal to a bias voltage of the circuit at both sides connected to terminals T1, T2. Then the capacitor 4 is charged through a resistor 8 and the capacitor 5 is charged through a resistor 9 respectively. Thus, diodes 6, 7 are reversely biased and the impedance is increased, then the coupling capacitor 3 is separated electrically from the capacitors 4, 5 or the like. Thus, even if the capacitance of the coupling capacitor is large, the circuit is operated quickly after application of power.